From: Warren Young <warren@etr-usa.com>
To: cygwin@cygwin.com
Subject: Re: get rid of getpwent? (Was: cygwin-1.7.28 getpwent header declaration changes ?)
Date: Sat, 08 Feb 2014 15:39:00 -0000 [thread overview]
Message-ID: <707CF923-5BCD-477F-A376-6E099E67697F@etr-usa.com> (raw)
In-Reply-To: <C1264DEE-1D5E-4F08-8DB5-D62A0EA4DCC0@etr-usa.com>
On Feb 8, 2014, at 8:19 AM, Warren Young <warren@etr-usa.com> wrote:
> On Feb 7, 2014, at 5:40 PM, Andrey Repin <anrdaemon@yandex.ru> wrote:
>
>> In either case, repeatedly requesting the same record in a short amount of
>> time will only test the system level cache.
>
> If that were true, moving the requested record around in /etc/passwd wouldn’t cause a 6x spread in test results. That’s O(N) type behavior, whereas a cache approaches O(1).
A clarification:
I agree that /etc/passwd is being cached for the entire test. My 12-line file is a bit over 1K, so it fits easily into a 4K RAM page. Also, I repeated my tests several times, so even the initial disk read is cached.
The fact that we see a 6x speed difference depending on where in the file — or RAM page, if you prefer — the target record is tells us that lookups are dominated by parsing time.
Parsing overhead shouldn’t exist for SAM or AD. They’re “pre-parsed.”
The equivalent overhead in SAM/AD terms is tree and index traversal, which should happen a lot faster than O(N).
--
Problem reports: http://cygwin.com/problems.html
FAQ: http://cygwin.com/faq/
Documentation: http://cygwin.com/docs.html
Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
next prev parent reply other threads:[~2014-02-08 15:39 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-06 7:29 cygwin-1.7.28 getpwent header declaration changes ? Marco Atzeri
2014-02-06 9:01 ` Corinna Vinschen
2014-02-06 10:20 ` Marco Atzeri
2014-02-06 13:00 ` Jan Nijtmans
2014-02-06 14:02 ` Corinna Vinschen
[not found] ` <CAO1jNws3H_Wbec=y_UoYkhrb5nMX7iT7_A5XaHcQKCw32o055g@mail.gmail.com>
2014-02-06 14:15 ` Fwd: " Jan Nijtmans
2014-02-06 14:28 ` Corinna Vinschen
2014-02-06 14:41 ` Corinna Vinschen
2014-02-06 14:13 ` Corinna Vinschen
2014-02-06 21:43 ` get rid of getpwent? (Was: cygwin-1.7.28 getpwent header declaration changes ?) Warren Young
2014-02-07 9:49 ` Corinna Vinschen
2014-02-07 12:50 ` Andrey Repin
2014-02-07 17:26 ` Warren Young
2014-02-07 18:20 ` Andrey Repin
2014-02-07 13:53 ` David Stacey
2014-02-07 17:51 ` Warren Young
2014-02-07 19:21 ` Corinna Vinschen
2014-02-09 16:10 ` Warren Young
2014-02-09 16:16 ` Corinna Vinschen
2014-02-09 16:31 ` Corinna Vinschen
2014-02-09 16:37 ` Ken Brown
2014-02-09 17:12 ` David Stacey
2014-02-10 10:48 ` Warren Young
2014-02-10 13:16 ` Peter Rosin
2014-02-10 22:05 ` Warren Young
2014-02-10 23:35 ` David Stacey
2014-02-11 2:35 ` Andrey Repin
2014-02-12 0:06 ` David Stacey
2014-02-12 2:06 ` Warren Young
2014-02-12 3:54 ` Eric Blake
2014-02-12 9:09 ` Corinna Vinschen
2014-02-12 12:05 ` Andrey Repin
2014-02-12 15:16 ` Richard
2014-02-12 16:24 ` Ken Brown
2014-02-12 17:05 ` Richard
2014-02-12 17:15 ` Andrey Repin
2014-02-12 20:49 ` Corinna Vinschen
2014-02-12 22:53 ` Christopher Faylor
2014-02-13 11:46 ` Corinna Vinschen
2014-02-13 14:35 ` Andrey Repin
2014-02-13 14:38 ` Christopher Faylor
2014-02-13 15:37 ` Corinna Vinschen
2014-02-13 15:48 ` Christopher Faylor
2014-02-13 16:09 ` Corinna Vinschen
2014-02-13 18:33 ` get rid of getpwent? Achim Gratz
2014-02-13 19:02 ` Andrey Repin
2014-02-13 20:41 ` Corinna Vinschen
2014-02-13 21:48 ` Achim Gratz
2014-02-14 9:46 ` Corinna Vinschen
2014-02-12 4:40 ` get rid of getpwent? (Was: cygwin-1.7.28 getpwent header declaration changes ?) Andrey Repin
2014-02-07 20:09 ` Warren Young
2014-02-07 20:25 ` Warren Young
2014-02-07 21:01 ` Corinna Vinschen
2014-02-07 21:30 ` Corinna Vinschen
2014-02-07 21:49 ` Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2014-02-08 10:38 ` Corinna Vinschen
2014-02-08 21:29 ` Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2014-02-09 1:29 ` Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2014-02-07 21:44 ` Larry Hall (Cygwin)
2014-02-07 22:45 ` David Stacey
2014-02-07 23:39 ` Larry Hall (Cygwin)
2014-02-08 0:50 ` Andrey Repin
2014-02-08 15:19 ` Warren Young
2014-02-08 15:39 ` Warren Young [this message]
2014-02-09 20:06 ` cygwin-1.7.28 getpwent header declaration changes ? Marco Atzeri
2014-02-09 20:20 ` Corinna Vinschen
2014-02-10 16:14 ` Marco Atzeri
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=707CF923-5BCD-477F-A376-6E099E67697F@etr-usa.com \
--to=warren@etr-usa.com \
--cc=cygwin@cygwin.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).